(Convener: Moriarty; Rapporteur: Poole)
7. In his Convener's report Moriarty described the current status of glasseel and elver monitoring which is currently taking place from the Imsa R., Norway in the north to the R. Minho, Portugal in the south. The need for regular data from the Mediterranean region was emphasized. The number of stations sending data into this study is now fourteen, including the Bay of Biscay. The years 1989 and 1990 have in general been very bad indeed and general been very bad indeed and current indications were that 1991 might be worse. The information presented showed with few exceptions a period of abundance in the twenty years preceding the 1980's followed by a severe drop in both catches and abundance indices in the 1980's.
The overall picture for 1989 and 1990 was of catches even lower than in the previous years. There was a slight improvement in catches in 1990 with eight stations showing an increase on 1989. Catches in the R. Yser rose from 30 kg in 1989 to 200 kg in 1990 but the other increases were much smaller in magnitude. There are now fewer glasseels arriving off the coast, especially in northern Europe. In comparison to the 1960's and 1970's the recruitment to the estuaries and rivers is now extremely low and is likely to be reflected in the catches and stocks of yellow eels in the rivers and lakes. He sounded a warning of the ongoing decline to the European governments and requested a greater research input towards a now serious situation.
8. Domingos presented data on fluctuations in the glasseel migrations in the Mondego Estuary, Portugal with particular reference to some abiotic factors. Official data were scarce prior to the enforcement of fishing regulations. Both passive and active methods of glasseel capture were assessed. It was noted that glasseel were present in the estuary throughout the whole year but peak catches always occurred during the official fishing season from November to February. Annual peaks in catch did not coincide. Highest catches were made at night with maxima at 01.00 hrs and declining rapidly after that. Lowest catches occurred in summer when the temperature and salinity are highest. However, high rainfall can decrease salinity and lead to increases in summer catches. Strong river flow caused by heavy rain prevents glasseel migrating upstream and hence results in low catches. In retrospect, the data show that while during the 1960's and 1970's the catches of glasseel were high, since then a decline has followed.
9. Desaunay presented data by Guerault on the evolution of glasseel migration in three French estuaries, the Loire, Villaine and Adour, from 1985 to 1990 which were used as a general indciator of the annual recruitment. The fishing methods and climatic factors were not consistent between the three estuaries. In the short term, it was found that the individual trends were rarely the same and the variation of the marine recruitment from year to year can differ between locations. In the mean term, over the period 1985 to 1990, all three estuaries showed decreasing recruitment. Since the 1970's the catch had decreased by a factor of 3.1 and the CPUE by a factor of 3.5. In discussion, Desaunay emphasized that even after 25 years it is still too early to relate glasseel recruitment to the yield of silver eels. Silver eel catches have remained relatively constant over the period of glasseel decline. It was also noted here that high flood levels decreased the fluvial glasseel catches and increased the marine catches. Drastic decrease in water temperature results in a clear decrease in catchability.
10. Analysis of data by Ben Abdallah, presented by Fontenelle, considered the influence of abiotic factors on glasseel abundance within the Loire estuary, examining the influence of tidal strength, water temperature and river flow. Time series analysis, smoothed moving averages and polynomials to discriminate between the tidal cycle component and the seasonal effects intra-annually and the remaining inter-annual trends seemed to be closely related to water temperature. It is important to try the analysis in warmer countries, such as Spain, Portugal and Morocco, to remove the temperature threshold (4°C). Caution was required in the use of fluvial weir/trap data as unknown quantities of juvenile eels from the estuary may also be included. True glasseels in the marine environment are needed for this analysis. It was concluded that where good longterm data exist, the time series analysis could be used as an abundance index.
11. McGovern and McCarthy discussed the migration of elvers into the R. Corrib. Their movements were monitored using low head elver traps and the glasseels were collected on low tide shore searches. Glasseels were recorded arriving on the shore from November and ascending into freshwater from April onwards. Biometrical analysis revealed that length and condition decreased from November to June and the pigmentation increased. The closer the tide was to midnight the higher the catches of elvers, regardless of tidal height and the catches appeared to be related to the tidal height seven days earlier. The migration into freshwater began after the temperature of 11°C was reached and the temperature difference between marine and freshwater was never more than 1.5°C. A distinction between the threshold of 4°C for movement of marine glasseels and 11°C for the movement into freshwater was made in the discussion. These are two different behavioural mechanisms.
12. Tesch presented his final data and from “Friedrich Heinke” on leptocephali trawl catches. Trawl catches from 1985 to 1988 gave 3 to 5 individuals per hour and 2 larvae per hour in 1989. These numbers are low compared to results from 1971 to 1977 (22 larvae per hour). Northern larvae were longer than southern larvae which confirmed earlier results. Tesch proposed that there was a stepwise reduction to leptocephali numbers from north to south, i.e. from Baltic to Biscay to Iberia. No connection between the stock reduction and oceanic currents has so far been found.
13. White and Knights described work that had just begun on the River Severn (England), funded by the National Rivers Authority. This will involve studies of elver recruitment and the effects of the elver fishery and of barriers on migration and recruitment to the catchment stock. Unlike the situation in some European estuaries, data on elver entry and fishing mortality have proved very difficult to obtain, although there is evidence of falling elver runs, especially in 1991. Further work is being carried out using traps to assess upriver migration and the value of eel-passes to improve recruitment into the catchment (and hence, ultimately, the potential breeding stock).
A call for research proposals under the EC Fisheries and Aquaculture Research (FAR) programme was then discussed. White and Knights proposed an international collaborative research programme using trapping techniques on weirs, sluices, etc. in underutilized catchments similar to the Severn. The practical and financial difficulties of FAR were mentioned and some members argued that effort should be put into processing data already available from other elver fisheries.
